1. Field of the Invention
This invention generally relates to an extruding die useful in hot-extrusion into aluminum or aluminum alloy shapes, and more particularly, to an extruding die, which is so improved as to permit production of extruded materials of higher dimensional precision, while meeting a demand for longer life.
2. Description of the Prior Art
A die serving to hot-extrude aluminum or aluminum alloy (which will be hereinafter simply referred to as Al or Al alloy) is useful under the high temperature and friction environment, and is thus limited as to its material to hot-working tool steel typically known as JIS SKD61.
However, the die made of the tool steel as described the above by itself causes the useful life to be shortened by cracking and seizure of a material to be extruded onto the die surface in the process of extruding, as well as high temperature wear or the like. The cracking, seizure and high temperature wear or the like as described the above are supposed to be factors contributing to surface folding of products and degradation of product quality inclusive of degraded dimensional precision, and the need for frequent exchange of dies also results in remarkably degraded productivity.
Various kinds of arts have been proposed in order to solve the above problems.
For instance, in Japanese Patent Laid-open No. 2-46914, there is disclosed the art of cladding a bearing part of the die with Co-group alloy.
In Japanese Patent Laid-open No. 8-281320, there is disclosed the art of applying carbide coating on a prospective die surface portion contacting Al or Al alloy.
In Japanese Patent Laid-open No. 7-155828, there is disclosed the art of applying zinc brittle-resistant coating by cladding or thermal-spraying the surface of a mandrel bridge part of the die with Ni-group alloy, Mo-group alloy, Co-group alloy or the like.
However, the above prior arts present the following problems respectively.
That is, using the art of cladding the die surface with the Co-group alloy as disclosed in Japanese Patent Laid-open No. 2-46914 controls die cracking and high temperature wear, while heat generated in the process of cladding causes the die to be locally heated to produce strain easily. The strain thus produced leads to degraded dimensional precision of extruded shapes.
Using the art of applying the carbide coating on the die as disclosed in Japanese Patent Laid-open No. 8-281320 is liable to cause the coating to peel off the die. Thus, there is the need for measures of grading the concentration of components in the range of a contact surface of the coating with the die. However, the above measures will be supposed to be variance with reality because of the need for a complicated process of applying the coating, together with high cost.
Using the art of only applying the predetermined alloy coating by thermal spraying as disclosed in Japanese Patent Laid-open No. 7-155828 does not attain sufficient adhesiveness between the alloy coating and the die, and causes the alloy coating to peel off so easily as to fail to produce the satisfactory longer life effect of the die.
It is an object of the present invention to provide an Al or Al alloy extruding die, which permits production of extruded materials of higher dimensional precision while meeting a demand for longer life of the die by preventing die cracking and high temperature wear more satisfactorily from occurring in the process of extruding, by means of applying high temperature wear-resistant alloy coating on a required portion of the die in such a manner as to permit less peeling without causing the die to produce strain.
To attain the above object, an Al or Al alloy extruding die in the first mode according to the present invention comprises Co-group alloy, Ni-group alloy, Cr-group alloy or like high temperature wear-resistant alloy coating applied by thermal spraying on a required die surface portion having been formed in the shape of a rough surface having surface roughness Rz of 5 xcexcm or more.
In the Al or Al alloy extruding die in the first mode, an Al or Al alloy extruding die in the second mode according to the present invention is characterized in that the die is held at a temperature in the range from 500 to 800xc2x0 C. for a predetermined period of time, after the above alloy coating has been applied on the above rough surface.
In the Al or Al alloy extruding die in the first mode, an Al or Al alloy extruding die in the third mode according to the present invention is characterized in that the alloy coating surface is so roughened as to have surface roughness Rz of 10 xcexcm or less.
In the Al or Al alloy extruding die in one of the first to third modes, an Al or Al alloy extruding die in the fourth mode according to the present invention is characterized in that the thickness of the alloy coating is limited to the range from 10 xcexcm or more to 200 xcexcm or less.